The present invention relates in general to hydraulic brake systems for land vehicles and in particular to a brake system and to a brake system control method for pressure control during automatic braking operations.
Hydraulic brake systems for land vehicles may be devised in such a way that, in addition to driver-controlled braking operations, they may carry out automatic braking operations that occur independently of an actuation of the brake system by the driver. Examples of such automatic braking operations include braking operations for acceleration spin regulation (ASR) that prevent individual wheels from spinning during the starting operation by targeted braking of the corresponding wheels, braking operations for an electronic stability program, whereby vehicle behaviour is controlled in extreme ranges by targeted braking of individual wheels, and braking operations for adaptive cruise control, in which for example through automatic braking of the vehicle defined speeds and/or distances from vehicles travelling in front are maintained.
Automatic braking operations are to occur in such a way that they are not perceived by the driver and/or do not cause any unwanted vehicle movements (for example jolting and/or pulling of the vehicle). These aims are difficult to achieve for several reasons.
Automatic braking operations conventionally run off at low brake pressures. In this case, interfering influences, such as for example unequal clearances between brake pistons and brake linings, unevenly worn brake linings, displaced brake pistons and/or brake linings etc., come particularly into play. During the operation of hydraulic brake systems having two brake circuits, such interfering influences are compensated during driver-controlled braking operations in that pressure equalization is possible between the brake circuits. This compensation is not available during automatic braking operations because in this case the two brake circuits are hydraulically separate from one another. Instead, during automatic braking operations both in brake systems having one brake circuit and in brake systems having two or more brake circuits it is necessary to compensate interfering influences separately for each brake circuit.
In order to allow automatic braking operations to run off comfortably, for example without jerky movements and/or pulling of the vehicle, it is desirable for the brake pressures, which exist in the brake circuits and produce the braking effect, to be adjusted as precisely as possible.